Flame spray applicator systems are used to spray a powdered material such as a thermoplastic (e.g. ethylene acrylic acid copolymers, polyethylene and derivatives) as a coating on a surface (e.g. aluminum). The powder material is entrained in a carrier gas (e.g. air) and delivered to an open atmosphere spray applicator where it is heated to its melting point by a flame (e.g. oxygen-propane) and is propelled against a preheated surface to be coated by the carrier gas.
Flame spray applicator systems for thermoplastic materials are disclosed in U.S. Pat. Nos. 4,934,595 and 4,632,309 issued to Reimer. A flame spray applicator system similar to that disclosed in the former patent is in commercial use. Such flame applicator systems are designed such that the powder material is contained in a conically shaped hopper proximate the spray applicator (spray gun), usually on the operator's back. The controls to operate the flame applicator system (i.e. gas regulators, shut off valves etc.) are numerous and are located on both the hopper and the spray applicator, making the device difficult to fabricate and operate. The inventors of the present invention discovered that, in using the Reimer device, the proximate location of the hopper to the spray applicator often caused the powder to heat up and fuse hindering flow from the hopper, especially when the coating operation was taking place in an enclosed environment. Also, when air was shut off to the spray applicator, the air could backflow through the hopper, rendering the powder airborne. The Reimer device was also found to include a rather elaborate system for delivering the carrier gas to hopper and then to the spray applicator which resulted in a tortuous air flow and a high pressure drop between the carrier gas supply and the spray applicator. This limited the amount of powder which could be entrained in the carrier gas and thus the efficiency of the system. The Reimer device uses a venturi at the base of the hopper to entrain the powder in the carrier gas, however, the pressure drop through the venturi was found to be quite high. Also, adjustment of the venturi tube at the base of the hopper was found to be cumbersome. Finally, the overall design of the flame spray applicator was found to be unnecessarily complex and expensive to machine.
Accordingly, an improved flame applicator system is provided which addresses the above discussed problems associated with the prior art.